Control system for continuous annealing lines and the like



D. c. NELSON 3,252,693

AND THE LIKE May 24, 1966 CONTROL SYSTEM FOR CONTINUOUS ANNEALING LINES 2 Sheets-Sheet 1 Filed May '2, 1963 AMPLlFIER Fig. I.

SERVO MOTOR CONTROL CONTROL Ship INVENTOR igdson ATTORNEY D. C. NELSON May 24, 1966 CONTROL SYSTEM FOR CONTINUOUS ANNEIALING LINES AND THE LIKE 2 Sheets-Sheet 2 Filed May '7, 1963 JOFPZOU q mON BY W ATTORNEY United States Patent 3,252,693 CONTROL SYSTEM FOR CONTINUOUS ANNEAL- IN G LINES AND THE LIKE Don C. Nelson, Aliquippa, Pa., assignor to Jones &

Laughlin Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed May 7, 1963, Ser. No. 278,634 6 Claims. (Cl. 266-3) This invention relates to apparatus for controlling a continuous annealing line for metal strip and the like. More particularly, the invention relates to a control system of the type described in which actual measured values of exit hardness, furnace temperature and the like are compared with the desired values for these factors to produce electrical signals for controlling the temperature of the annealing furnace and/ or the speed of the strip mafirst hot rolled, pickled and then cold reduced, during which time its grain structure is crushed and strained. This results in a product that is very hard and brittle, meaning that it must be softened or recrystallized by annealing in order that it can be formed into can ends, bodies and the like. In any annealing line, the major property to be controlled is-the final or exit hardness of the strip. Factors which affect this exit hardness include the composition of the strip, the gage or thickness of the strip, the degree of the cold working, the speed at which the strip is moved through the annealing furnace, the annealing furnace temperature, and others. Certain of these factors will be fixed such as the composition of the strip and its gage, as well as the degree of cold working. In order to compensate for changes in these fixed factors from coil to coil to insure a predetermined exit hardness, the line speed and/ or furnace temperature must be varied.

In the past, the exit hardness was determined by running the strip through the annealing line and by manually checking the hardness at the exit end with a conventional hardness testing machine, If the hardness did not meet order specifications, factors such as the furnace temperature settings, the cooling rate or the line speed were varied manually, and the foregoing process repeated as many times as necessary with a new hardness reading being taken after the strip had passed through the line. This method not only takes considerable time, but also results in a considerable waste of material which has passed through the line before the hardness reading can be taken; and, in any event the hardness control is only approximate.

As an overall object, the present invention seeks to provide a control system for a continuous annealing line wherein the furnace temperature and/or line speed are automatically regulated to control the exit hardness.

Another object of the invention is to provide a servo system for a continuous annealing line wherein the hardness of metal strip material is continually measured at the output of the annealing line by a non-contacting hardness gage, the gage being adapted to produce an electrical signal in the servo system for controlling line speed and furnace temperature to thereby maintain a constant predetermined exit hardness.

A further object of the invention is to provide a control system of the type described which computes the proper line speed and furnace temperature for an annealing line from electrical signals representing such factors 3,252,693 Patented May 24, 1966 as predetermined desired line speed, desired exit hardness, and desired gage, and by comparing the predetermined desired factors with electrical signals representing the actual measured values of these factors to produce error signals for either increasing or decreasing line speed and/ or furnace temperature to produce the correct exit hardness.

The invention, in its simplest form, comprises a servo system wherein an electrical signal which varies as a function of the actual output hardness of the strip material from the annealing'line is used to control the line speed and/ or temperature of the annealing furnace to maintain a constant output hardness. Preferably, two servo loops are employed, one of which utilizes an electrical signal proportional to actual exit hardness for controlling the speed of the line, and the other of which employs this same signal to control furnace temperature. In the operation of the system, both the line speed and fuel input to the furnace will be varied in response to a variation in output hardness. Since, however, the furnace temperature cannot be controlled directly, but only the fuel or other heat-producing energy input to the furnace, a considerable time delay is encountered in changing furnace temperaure. As a result, the line speed variation will initially effect the desired change in hardness, followed by a change in furnace temperature. If it is assumed, for example, that the hardness falls below the desired value, the line speed will increase. At the same time the supply of fuel or heat-producing energy to the furnace will be decreased. Due to the latent heat of the furnace, however, it will take a considerable amount of time for it to cool, during which time the line speed is increased over the point where it will be at the desired furnace temperature of effect the desired hardness. As the furnace cools, however, exit hardness will tend to increase, meaning that the line speed and supply of fuel to the furnace will be decreased until an equilibrium point is reached. In this manner, the dual servo loops continually hunt for the equilibrium condition during which time line speed is initially varied followed by a variation in furnace temperature.

In accordance with another aspect of the invention, it has been found that the desired exit hardness H of steel strip used in the manufacture of tinplate can be determined from the following general algebraic equation:

k k k;,, k.,, k k and k are constants;

U =annealing line speed in ft./min.;

t= thickness of the annealed strip in inches;

T =predetermined desired heat zone furnace temperature in F.;

C=carbon content of the steel in percent; and

P phosphorus content of the steel in percent.

Although the other constituents of the strip composition will affect its hardness to some degree, it has been found that the carbon and phosphorus contents are the most critical; and, accordingly, these only are taken into consideration in the foregoing equation.

Accordingly, in accordance with a second embodiment of the invention shown herein, the desired exit hardness, the carbon and phosphorus percentages of the strip, the desired line speed and the gage of the strip are recorded on a punch card in the form of perforations, and apparatus is employed to convert the indicia represented by the perforations into electrical signals. These signals are fed into a computer together with a signal representing the desired furnace temperature. The computer will then compute the fore-going equation or its equivalent to produce an error signal for controlling the furnace temperature and/or line speed. At the same time, apparatus is employed for producing electrical signals proportional to the actual gage of the strip material passing through the annealing line, the actual speed of the strip material, the actual furnace temperature, and the actual exit hardness. These signals are compared with those fed into the computer to produce error signals for correcting any discrepancy between desired values and actual values. As was mentioned above, in all cases, the main property to be controlled is the exit hardness; and the computer is designed whereby the signal representing the actual output hardness will override all other signals to control furnace temperature and line speed.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a schematic circuit diagram of one embodiment of the invention wherein servo loops are employed to control line speed and/or furnace temperature as a function of output hardness; and

FIG. 2 is a block schematic circuit diagram of another embodiment of the invention wherein not only exit hardness but also the carbon and phosphorus percentages of the strip material passing through the annealing line, the desired line speed, and the gage of the strip are compared in a computer for the purpose of controlling actual line speed.

Referring now to the drawings, and particularly to FIG. 1, metal strip material passes through an annealing furnace schematically illustrated by the block 12, the strip being driven through the furnace by means of drive rolls 14 connected to a drive motor 16. The furnace 12 is heated by means of hydrocarbon gas, the gas inlet to the furnace being schematically indicated at 18. Gas flowing through the conduit 18 and, hence, into the furnace 12 is controlled by means of a valve 20. Alternatively, rapid heating of the furnace 12 can be effected by means of an induction coil 22, the current through this coil being controlled by means of a potentiometer 24.

At a point removed from the exit side of the furnace 12 is a non-contacting hardness gage 26. The hardness gage 26 may be of the type shown in copending application Serial No. 828,358, filed July 2O, 1959, now aban doned but is preferably of the type shown in applica tion Serial No. 217,345, filed August 16, 1962, both of said applications being assigned to the assignee of the present application. Essentially, the hardness gage described in the aforesaid applications comprises apparatus for bombarding the surface of the metal strip with radio active energy (i.e., beta rays) which will not penetrate through the thickness of the strip, and means for collecting the backscatte-red radiation reflected from the surface of the strip to generate an electrical current, the magnitude of which is indicative of the hardness of the strip. In this manner, an electrical signal is derived on leads 28 which varies as a function of the hardness of the strip material 10 after passing through the annealing turn-ace 12. This signal is amplified in amplifier 30 and applied to two bridge circuits 32 and 34.

The bridge 32 may be called a speed bridge and comprises four impedances connected end-to-end, one of said impedances comprising the hardness gage 26. In another leg of the bridge 32 is a potentiometer 36 connected through a mechanical linkage 38 to a servomotor 40. The bridge is completed by two resistors 42 and 44, the resistor 44 being variable as shown. A source of voltage, not shown, is applied to the input terminals 46 and 48 of the bridge, and an output signal -is derived across leads 50 and 52. This signal is applied to a servomotor control circuit 54 which controls the servomotor 40, thereby causing it to rotate in one direction or the other.

In the operation of the speed bridge circuit 32, the variable resistor 44 is adjusted for a particular hardness,

and the voltage across this resistor comprises an electrical signal indicative of the desired output hardness of the strip material from the annealing furnace 12. As long as the hardness detected by the gage 26 is equal to the desired hardness as determined by the position of variable resistor 44, the voltage across leads 50 and 52 will be zero and the servomotor 40 will remain stationary. If, however, the hardness should rise or fall below that determined by the setting of the variable resistor 44, an output signal will appear across leads 50 and 52 and will be applied through circuit 54 to the servomotor 40, thereby rotating the movable tap on potentiometer 36 until the bridge is again balanced, at which time the servomotor 40 stops. During rotation of the servomotor 40, it also rotates the movable tap on a potentiometer 56 included in the motor control circuit 58 for drive motor 16, thereby increasing or decreasing the speed of the strip 10, depending upon the direction of rotation of servomotor 40.

With reference, now, to the bridge 34, it may be called a temperature bridge and includes a potentiometer 60 in one leg of the bridge together with two resistors 62 and 64, the resistor 64 being variable and adjustable with resistor 44 to the desired hardness. voltage across resistor 64 comprises an electrical signal indicative of the desired output hardness of the strip material 10. A source of voltage, not shown, is applied to input terminals 66 and 68, and an output appears across leads 70 and 72 when the bridge becomes unbalanced. The signal across leads 70 and 72 is applied to servomotor control circuit 74 which, in turn, is used to control a second servomotor 76. The servomotor 76 is connected through linkages 78 and 80 to the potentiometers 60 and 24, respectively. Likewise, it is connected through linkage 82 to valve 20 which controls the flow of fuel gas through the conduit 18 into the furnace 12.

Elf the temperature bridge 34 becomes unbalanced, a signal will appear across leads 70 and 72 to rotate the servomotor 76 in one direction or the other, depending upon whether the hardness of the strip 10 increases or decreases. If the hardness increases, then the servomotor -76 will be rotated to further open the valve 20 and increase the supply of gas to the furnace 12. At the same time, the movable tap on potentiometer 24 is adjusted to increase the current through the induction coil 22. A fall in hardness of the strip 10 will effect the opposite result. That is, the gas supply in conduit .18 will be decreased as will the current through the coil 22.

In operation, as long as the hardness of the strip 10 detected by the gage 26 remains at the desired hardness as determined by the resistors 44 and 64, the bridges 32 and 34 will be balanced and the servomotors 40 and 76 will remain stationary. If, however, the hardness of the strip should increase, it means that each incremental length of the strip 10 does not remain in the furnace (12 long enough or that the temperature of the furnace is not great enough. Under these conditions, both bridges 32 and 34 will become unbalanced. Unbalance of the bridge 32 will cause the servomotor 40 to rotate the movable taps on potentiometers 36 and 56, thereby decreasing the speed of the strip 10 while again balancing the bridge 32 through a change in position of the tap of potentiometer 36. At the same time, unbalance of the bridge 34 will cause the valve 20 to open further to supply a greater quantity of gas to furnace 12. Simultaneously, the current through the induction coil 22 will be increased to assist in rapidly raising the temperature of the furnace. As soon as the hardness of the strip 10 begins to decrease, the bridges 32 and 34 will again become unbalanced, thereby increasing the speed of the strip 10 and decreasing the supply of fuel to the furnace 12. This action will continue until an equilibrium point is reached where the hardness remains at its desired value.

If the hardness should fall rather than increase, the foregoing procedure is repeated in reverse fashion with the system again hunting for an equilibrium condition.

Here, again, the i It will be noted that in the operation of the system, both the line speed and fuel input to the furnace are varied immediately in response to a variation in output hardness. Since, however, the furnace temperature cannot be controlled directly, but only the fuel or other heat-producing energy input to the furnace, a considerable time delay is encountered in changing the furnace temperature. As a result, the line speed variation will initially effect the desired change in hardness, followed by a change in furnace temperature. However, as the furnace temperature is changed, the line speed will be varied in the reverse sense until the aforesaid equilibrium condition is reached.

Referring now to FIG. 2, the annealing line is shown in much greater detail. Cold reduced coils of steel 11%) and 112 are first loaded into coil holders used to pay off steel into the continuous annealing line. Two coil holders are employed. so that the one coil may be made ready for the operation while operating on the other coil. The coil holders are followed by a welder as at 114 which is used to weld the tail end of one coil in the process to the beginning of a succeeding coil.

The steel next passes through an X-ray thickness gage 116 and a butt weld detector into electrocleaning tanks 1.18 where the residual oils from the cold reduction process are removed. In the electrocleaning process, the strip is immersed in an alkaline, phosphate or silicate solution and subjected to bi-polar electrolytic action to remove all soil from the surface of the strip. The steel then passes through a scrubber as at 120 where it is brushed with rot-ary brushes and rinsed with water. From the scrubber at 120, the steel passes into a deep rinse tank and final rinse sprays, not shown, and is thereafter dried as at 122 and passed through a first bridle 124. The entry end of the continuous annealing line from the coil holders to the first bridle 124 operates as a separate section of the line with its own independent speed control. The speed of this section, however, can be electrically matched to the speed of the continuous annealing furnace if desired.

In order to maintain the continuous annealing process at a steady-state condition, a slack producer is provided between the entry end of the line and the furnace. The slack producer or looper 126 supplies the steel necessary to maintain a continuous process while the welding of the ends of two different co-ils is performed at 114. That is, the entry looper provides enough strip storage so that the annealing line can run continuously at a speed of at least 1500 feet per minute during the Welding operation. Following the entry looper 126 is a second bridle 128; and following the bridle 128 is an entry guide loop 130 which acts as: (1) a shock isolation device to prevent the shock from the entry end due to starting and stopping of the strip from reaching the furnace 132 where the strip is under elevated temperatures, and (2) it acts to re-center the strip in the center of the line prior to entering the furnace section.

The furnace section starts with a third bridle 134 and extends to a fourth bridle 136 on the other side of the furnace 132. Between these two points, the main part of the annealing process is performed. Immediately following bridle 134 is a tension device, not shown, which acts to control the strip tension at a preset value by either acelerating or decelerating bridle 134 in a v-ernier fashion. The strip then passes through the entry steering roll 140 and through furnace seal rolls, not shown. The seal rolls are provided in the wall of the furnace to maintain a positive pressure of a gaseous atmosphere in the continuous annealing furnace which prevents oxidation of the strip while it is at elevated temperature. The strip first passes through the heating zone 142 which, in the embodiment of the invention described herein, consists of six vertical passes. Vertical rows of fifteen burners each are situated in between each of the vertical strands of strip. Also provided is a vertical row of fifteen burners ahead of the first strand and after the sixth strand. These burners are arranged in zones of control in various manners. In some furnaces each vertical row of burners may be a control zone, while in other furnaces a combination of vertical rows of burners are control zones. In addition to the burners described above, one or more induction heating coils, schematically illustrated at 144 are included in the heating zone whereby the temperature of the strip may be rapidly increased. That is, in order to raise the temperature of the strip with the use of burners, the valves controlling the feed of gas to the burners must be regulated, after which a considerable amount of time will be required to actually raise the temperature of the strip. In the case of induction heating apparatus, however, the temperature of the strip will be raised almost immediately upon an increase of current to the induction heating coil.

From the heating zone 142, the strip passes into a soaking section 146 where the strip is held at the annealing temperature while it passes through eight vertical strands for the embodiment shown herein. The heat within the soaking section may be augmented by electrical resistance heating or any other suitable heating means.

From the soaking section 146 the strip then passes into the control cooling section 148 consisting of six vertical passes. This zone also uses electrical resistance heating to bring its temperature up during start-up operations. However, once the annealing process has started, the zone is normally cooled by drawing room air through tubes which extend through the zone in between each strand of the strip. That is, the strip is cooled in this zone by blowing air upon its surface.

' The amount of air that is blown against the strip is controlled by the temperature of the strip leaving the control zone 148.

From zone 148, the strip passes into the fast cooling zone 150 which consists of twelve vertical strands. From zone 150 the strip passes out of the furnace 132 to bridle 136. Above the bridle 136 is a non-contacting hardness gag-e 152 similar to that shown in connection with FIG. 1.

From the hardness gage 152 the strip passes to a delivery guide loop 154 which serves the same purpose as the entry guide loop 130, and then to a fifth bridle 156. From bridle 156 the strip passes into an exit looper 158 and then to a sixth bridle 160. From bridle 160 the strip passes through a sample punch, a pinhole detector, an X-ray thickness gage, and through a delivery shear, all of which are not shown herein, to the tension reels 162 and 164 on which the annealed strip is coiled for delivery to the next operation.

The output signals from the X-ray thickness gage 116 and the hardness gage 152 are anal-0g signals; and, accordingly, these are converted into digital signals by analog-to-digital converters 166 and 168, respectively. The temperature within the heating zone 142 of furnace 132 is sensed by a temperature measuring device 170, such as a thermocouple, and its analog output signal is also converted into .a digital signal by analog-to-digital converter 172. Finally, the actual line speed is sensed by a tachometer 174 connected through linkage 176 to one of the line rolls. The output of the tachometer 174, in turn, is converted into a digital signal by an anal-og-to-digital converter 178.

The desired exit hardness of the strip material, the carbon and phosphorus percentages of the strip, the desired line speed, and the gage of the strip are recorded on a punch card 180 in the form of perforations. The punch card is inserted into a tab card reader 182 which will convert the indicia represented by the perforations on the punch card 180 into electrical signals on leads 184, 186, 188 and 190 which are connected to a master computer, generally indicated at 192. The signal on lead 190 will be a digital signal representing the carbon and phosphorus percentages of the strip, that on lead 188 will be a digital signal representing the desired exit hardness of the strip material from the annealing line; that on lead 186 will be the desired or predetermined strip speed; and that on lead 184 will represent the gage of the strip material entering the annealing line.

The strip material is moved through the annealing lines by drive motors connected to the various rolls in the bridles and loopers. Only one such drive motor is shown in the drawing and is indicated schematically at 194. Drive motor 194, in turn, is controlled through line speed control circuit 196 by a control signal from the computer 192 on lead 198. The manner in which the control signal on lead 198 is produced will be hereinafter described.

As shown, the computer 192 has two output leads 198 and 200, the second of which :controls the furnace temperature through a furnace control circuit 202. Circuit 202 controls valves 204 which admit gaseous fuel to the burners of the furnace and also the induction heating coil, generally indicated at 144, which is used to rapidly raise the temperature of the strip when necessary.

In order to initially set the furnace temperature, a furnace control means 208 is adjusted to produce a signal which is converted into a digital signal in analog-to-digital converter 210. This signal is fed into the computer 192 together with the signals on leads 184-190. Signals fed into the computer, therefore, represent the annealing line speed in feet per minute on lead 186 (U); the thickness of the annealed strip in inches on lead 184 (t); the predetermined desired heat zone furnace temperature from circuit 210 (T the desired exit hardness on lead 188 (H and the phosphorus and carbon contents of the steel on lead 190 (C and P).

If the computer then determines that:

then it is known that the furnace temperature and line speed are correct. If the foregoing equation is not satisfied, however, it is known that the line speed and/ or furnace temperature must be varied. In the practice of the invention, the line speed is initially varied, and thereafter the temperature of the furnace is varied. This is due to the fact that it takes a period of time in order to change the temperature of the furnace; whereas the line speed may be varied immediately. If the gage of the strip on card 180 does not correspond with the actual gage measured by X-ray thickness :gage 116, then the signal on lead 184 will not correspond to that at the output of circuit 166, and a binary subtractor 212 will produce an error signal on lead 214 to the computer to indicate the variance in gage. Similarly, if the desired strip speed does not correspond to the actual strip speed, then the signal on lead 186 will be subtracted from that from circuit 178 in binary subtractor 216 to produce an error signal on lead 218 to the computer. The same is true of furnace temperature. That is, if the actual furnace temperature as indicated by the signal at the output of circuit 172 does not correspond with that from circuit 210, then binary subtractor circuit 220 will produce an error signal on lead 222 to inform the computer of the actual temlperature. Thus, the line speed and the temperature of the furnace will be initially determined by a comparison of the actual and measured values of gage, strip speed, furnace temperature, and the composition of the strip. If, from this information, the equation outlined above does not balance due to the fact that the actual measured hardness at the output of circuit 168 does not equal the desired hardness on lead 188, the binary subtractor 224 will produce an output signal on lead 226 to the computer 192 to correct the matter by producing 8 control signals on leads 198 and 200 to the circuits 196 and 202, respectively.

If, for example, the actual measured hardness as determined by hardness gage 152 is below the desired hardness as indicated by the signal on lead 188, it is known that the strip is too soft. Accordingly, the computer will produce a signal on lead 198 to increase the speed of the drive motor 194 whereby the period of time that the strip remains in the furnace will be reduced. At the same time, a signal on lead 200 will reduce the supply of fuel to the gas burners in the furnace to reduce its temperature. After the temperature has been reduced, the computer will then reduce the line speed again. in a similar manner, if the actual exit hardness as determined by the hardness gage 152 is above the desired exit hardness, then the computer 192 will produce a signal on lead 198 to slow down or reduce the speed of the drive motor 194 whereby the strip will remain in the annealing furnace longer. At the same time, a signal is produced on lead 200 to increase the supply of gas to the burners, and at the same time the induction coil 144 is energized to rapidly raise the temperature of the strip.

It can thus be seen that the present invention provides a means for automatically controlling the desired exit hardness of strip material in a continuous annealing line. Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

I claim as my invention:

1. In a continuous annealing line having variable speed drive means for moving a continuous length of metal strip through the annealing line, the combination of a non-contacting hardness gage capable of producing an electrical signal which varies in proportion to the actual output hardness of the strip material from the annealing line, and electrical servo means responsive to said electrical signal for controlling the speed of said variable drive means.

2. In a continuous annealing line having an annealing furnace therein, the combination of a non-contacting hardness gage capable of producing an electrical signal which varies in proportion to the actual output hardness of the strip material from the annealing line, and electrical servo apparatus responsive to said electrical signal for controlling the temperature of said annealing furnace.

3. In a continuous annealing line having an annealing furnace therein and variable speed drive means for moving metal strip material through the annealing line, the combination of a non-contacting hardness gage capable of producing an electrical signal which varies in proportion to the actual output hardness of the strip material from the annealing line, and electrical servo apparatus responsive to said electrical signal for controlling the speed of said variable speed drive means and the temperature of said annealing furnace.

4. In a continuous annealing line having variable speed drive means for moving a continuous length of metal strip material through the annealing line, the combination of apparatus for producing a first electrical signal proportional to the desired output hardness of the strip material from the annealing line, a non-contacting hardness gage capable of producing a second electrical signal-proportional to the actual output hardness of the strip material from the annealing line, and means for comparing said first and second signals to produce an electrical signal for controlling the speed of said drive means.

5. In a continuous annealing line having an annealing furnace therein and adapted to anneal continuous lengths of metal strip material, the [combination of apparatus for producing a first electrical signal proportional to the desired output hardness of the strip material from the annealing line, a non-contacting hardness gage capable of producing a second electrical signal proportional to the actual output hardness of the strip material from the annealing line, and means for comparing said first and second signals to produce an electrical signal for controlling the temperature of said annealing furnace.

6. In a continuous annealing line having an annealing furnace therein and variable speed drive means for moving metal strip material through the annealing line, the combination of a radiation emitting hardness sensing device for producing an electrical signal which varies as a function of the actual output hardness of the strip material from the annealing line, and electrical :servo apparatus responsive to said electrical signal for controlling the speed of said vaniable speed drive means and the temperature of said annealing \furnace.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Continuous Annealing 60 Tons Per Hour of Tin 10 Plate, reprint from Iron and Steel Engineer, February,

JOHN F. CAMPBELL, Primary Examiner.

15 WHITMORE A. WILTZ, Examiner. 

1. IN A CONTINUOUS ANNEALING LINE HAVING VARIABLE SPEED DRIVE MEANS FOR MOVING A CONTINUOUS LENGTH OF METAL STRIP THROUGH THE ANNEALING LINE, THE COMBINATION OF A NON-CONTACTING HARDNESS GAGE CAPABLE OF PRODUCING AN ELECTRICAL SIGNAL WHICH VARIES IN PORPORTION TO THE ACTUAL OUTPUT HARDNESS OF THE STRIP MATERIAL FROM THE ANNEALING LINE, AND ELECTRICAL SERVO MEANS RESPONSIVE TO SAID ELECTRICAL SIGNAL FOR CONTROLLING THE SPEED OF SAID VARIABLE DRIVE MEANS. 